1. Field of the Invention: The present invention relates to non-aqueous dispersions of polymeric microparticles, and to the microparticles themselves. The invention also relates to coating compositions containing the microparticles and to coated articles derived therefrom.
2. Brief Description of the Prior Art: Non-aqueous dispersions of polymeric microparticles which are prepared by free radical addition polymerization of ethylenically unsaturated monomers in a diluent or in an organic liquid are known in the art. Polymerization is usually conducted in the presence of a dispersion stabilizer, one portion of which is solvated by the organic liquid and one portion of which is compatible with the polymeric microparticles. U.S. Pat. No. 3,514,500 describes such dispersions. The bond between the stabilizer and the polymeric microparticle may be simply an attraction due to similar polarity between the two.
U.S. Pat. No. 3,607,821 also describes non-aqueous dispersions of polymeric microparticles prepared in a manner similar to that of U.S. Pat. No. 3,514,500 but in which the dispersion stabilizer contains ethylenically unsaturated double bonds which react with the polymerizing ethylenically unsaturated double bonds in the monomer to form a more stable dispersion.
The above-described techniques for preparing non-aqueous dispersions of polymeric microparticles can be used to prepare dispersions of crosslinked polymeric microparticles. For example, as disclosed in U.S. Pat. No. 4,147,688, an ethylenically unsaturated monomer mixture containing at least two monomers which are difunctional with regard to one another such as glycidyl methacrylate and methacrylic acid can be copolymerized in an organic diluent such as pentane in the presence of one of the dispersion stabilizers mentioned above to produce crosslinked polymeric microparticles. The microparticles have been found to be useful as flow control agents in coating compositions. One disadvantage of these crosslinked polymeric microparticles is that they can cause a yellowing of clear coats, particularly clear coats which are applied over pigmented base coats in automotive top coat applications.